In engine mounts of this kind, the spring characteristics of an engine suspension can be optimally designed by appropriate configuration of the engine mounts and selection of the rubber quality, and also the damping inherent in the hysteresis of the rubber elastic peripheral walls can be supplemented by suitable design of the hydraulic damping, so that there are optimal conditions with respect to oscillation damping of the engine suspension also. In this way the requirement of motor vehicle construction is met, that it be possible strongly to damp lower frequency high amplitude oscillations of the engine casing, and allow high frequency oscillations with low amplitude, e.g. 0.1 mm, of the engine casing to pass undamped as much as possible.
From German Pat. No. 945,899, there is known a liquid hollow spring device with intrinsic damping, the device presenting a main chamber and an extension chamber, filled with a flow agent and connected via ports in a partition that serves as a supporting wall or element, with the main chamber consisting of a hollow spring element of rubber elastic material and the extension chamber being defined by a rubber elastic diaphragm. In this known arrangement the extension chamber only performs the task of receiving liquid forced from the main chamber and returning it thereto, such that the elastic deformation of the diaphragm contributes only slightly to the spring. It is a disadvantage that the space required for the extension chamber is not exploitable for the main function of the engine mount, namely the spring function.
A basic problem to which the instant invention is directed is to make use of an auxiliary chamber, somewhat analogous to that which accommodates the extension chamber of such known hollow springs, for a spring function. Thus, the space that accommodates the auxiliary chamber is used not only for the damping function by receiving and restoring fluid from and to the main chamber, but also advantageously for the spring function. In engine mounts in accordance with the invention, advantageously peripheral walls made as thrust springs are adheringly joined, for example by vulcanizing, with external conical surfaces of the supporting element or carried by the supporting element, and are joined also with internal conical surfaces of end walls of the device, or vice versa with inner conical surfaces of the supporting element or carried by the supporting element and external conical surfaces of the end walls, or there are combinations of these possibilities. If there are external conical surfaces of the supporting element and inner conical surfaces of the end walls, it is simple to use a unitary vulcanized rubber-metallic part. If there are internal conical surfaces of the supporting element and external conical surfaces of the end walls, the engine mount is advantageously made of two opposedly stressed rubber-metallic parts with a partition held between them. The connection of the end walls can be effected by means of a pin that passes through them and intermediate spacing tubes, whereby these parts pass through the partition. In this way a gap formed between a center hole of a partition and a spacing tube can function as a choke opening between auxiliary and main chambers separated by the partition. This gap can be made as a laminar gap by connection of the partition with a sheath, and its choke resistance can be adapted to different conditions by changing the diameter of the spacing tube.
The partition can be rigid, or it may be made as a rubber elastic partition, and it can be adheringly connected to the supporting element and a sheath which, together with a connecting pin, constitutes a choke gap. In this way the sheath can be movable with respect to the supporting element, and, for example, it can be immovable, by stressing it between spacing tubes. A rubber elastic partition can act as a thrust spring in the limited stroke-end zone of an end wall and be integral with a peripheral wall.
Because of the rigid connection of the two end walls of the device, the axial spring paths of the end walls with reference to the supporting element are equal to each other. The changes of volume of the main and auxiliary chambers that are caused by a specific spring path with balanced liquid pressure in the main and auxiliary chambers can be like or different, from suitable configuration of the peripheral walls and possibly of an elastic partition. If a decrease in volume of the main chamber is greater than the volume increase in the auxiliary chamber, the balanced liquid pressure moves outward with corresponding bulging of the peripheral walls. If a volume increase of the main chamber is greater than the volume decrease in the auxiliary chamber, the balanced liquid pressure drops with a corresponding inward contraction of the peripheral walls, whereby a vacuum can develop and cavities will form. Such cavities, or cavities intentionally produced, e.g. by incomplete filling, can serve in an engine mount strongly to damp low frequency oscillations with great amplitude and to allow high frequency low amplitude oscillations to pass, without exchange of liquid between the main and auxiliary chambers, hence without liquid damping. The same effect can be managed also with a readily movable partition whose stroke is narrowly limited. Inside the chambers there can be cavities closed off from the liquid by a diaphragm or diaphragms, the cavities being filled with gas at a selected pressure, or preferably vented to the outside. Pressurized liquid can be charged into the chambers in order to expand the peripheral walls from the beginning and to prevent production of a vacuum, if this is not wanted.
In one embodiment of an engine mount (to be hereafter described and shown) in accordance with the invention, a rubber elastic partition is adheringly joined with an internal surface of a supporting element and an external surface of a sheath which at the same time is adheringly joined with the end wall that is away from the engine. The sheath, along with a spacing tube associated with the rigid connection of the end walls, forms an annular choke gap whose form and size determine the magnitude of the hydraulic damping forces. In transverse movements that exceed the width of the choke gap, of an engine borne by the engine mount, there is the possible drawback of hard impact of the sheath on the spacing tube, and the radial rigidity of the engine mount is substantial. The engine mount of a further embodiment avoids these drawbacks in that a rubber elastic partition that is adheringly joined with a surface of the supporting element presents a collar at the end of a neck, which collar, together with a bolt that connects the two end walls or with a spacing tube held by the bolt, forms an annular gap which serves as a choke opening. The collar seated on the end of the neck advantageously imposes a relatively slight resistance to transverse movements, whereby the engine mount has less transverse rigidity, which can be effected to a desired degree by suitable configuration of the neck and collar.
With balanced fluid pressure in the main and auxiliary chambers, the changes in volume of the main and auxiliary chambers caused by a specific spring path of the engine mount may be equal to each other or different. If there are differences in volume, these can be balanced in an engine mount of the last mentioned embodiment by axial relative movements of the collar, where the collar and the neck are given suitable elastic resilience in an axial direction. Such axial resilience can likewise serve to accept high frequency oscillations with low amplitudes without any appreciable exchange of liquid between the main chamber and the auxiliary chamber, hence without any appreciable hydraulic damping. Oscillations with low amplitudes may also be accommodated by foamed structures in the main and/or auxiliary chambers, preferably disposed on the chamber walls, without occurrence of hydraulic damping, or not in any degree worth mentioning.
The invention also relates to hydraulically damped rubber elastic engine mounts designed for cutout of the hydraulic damping in case of high frequency oscillations. As previously mentioned, in use of engine mounts of this kind for automotive vehicle engines, it is desirable that low frequency high amplitude oscillations of the engine be strongly damped, and that high frequency, particularly acoustic, oscillations with minimal amplitudes be allowed to pass without liquid damping. In one embodiment it is proposed by way of example that hollow chambers closed off by diaphragms be provided for this purpose, the chambers being filled with gas or vented to the outside. The proposed chambers must impose a relatively high defined resistance to a forcing of the diaphragms, and they must be small, in order that even with low amplitudes of vibration of the motor mounting the pressure needed for hydraulic damping can build-up in the liquid chambers.
If for the purpose of fast build-up of pressure a chamber filled with gas at high pressure is provided, there is danger of a diffusion of the gas through the diaphragm into the liquid chambers, with loss or pressure in the gas chambers, and the resistance of the gas chambers against forcing in of the diaphragms will drop in a short time to undefined levels, and the characteristics of the hydraulic damping forces will be harmfully affected.
A further embodiment of the instant invention is addressed to the problem of further development of the engine mounting in accordance with the invention by a construction where high frequency oscillations of minimal amplitude will be effectively passed with operational reliability and cutting out of hydraulic damping. This problem is solved by providing a construction wherein one or more of the end walls present, in a double-wall arrangement, an outer fixed wall and an inner diaphragm-like yielding wall which is sealed off with reference to the outer end wall, the inner wall being fixed by means of rubber elastic edges to the outer wall and bearing on the outer wall by means of elastic projections through whose deformation resistance the yielding of the inner wall is defined. Preferably the intermediate space defined by the outer and inner walls presents venting ports that lead to the outside.
Thus advantageously in the liquid chambers there is a steady uniform build-up of the pressure needed for hydraulic damping in the case of greater amplitudes, because the yielding of the inner wall is precisely defined by the mechanical elasticity of the rubber elastic projections. On the other hand, the yielding of the inner wall, with suitable dimensioning, cuts out the hydraulic damping in case of high frequency oscillations of minimal amplitude, of the order of magnitude of a few tenths of a millimeter.
The outer wall of a double-walled end wall is advantageously provided with a depression that has conical transition surfaces, and the inner wall is made as a vulcanized rubber-metallic part consisting essentially of a metallic plate and a surrounding rubber edge, whereby the rubber edge is fixed to the outer wall and presents projections that are applied to the mentioned conical transition surfaces and deformed when the inner wall approaches the outer wall, with increasing resistance up to a blocking of the movement of the inner wall.
In the stroke-limited end position that is thus brought about, the inner wall can be thought as a fixed wall, and with great amplitudes the specified pressure in a liquid chamber for the stroke velocity of the end walls with respect to the supporting element can be developed to the full. In an engine mount whose liquid chambers have a connecting bolt passing through them to connect the end walls, the inner wall of a double walled end wall is advantageously made as a rubber-metallic part consisting of a metallic annular plate and rubber rings adheringly joined thereto on the inner and outer peripheries, with the bolt passing through. The chamber formed by the inner and outer walls of a double-walled end wall can be filled with gas at pressure high enough so that a change of pressure, e.g. by diffusion of the gas into the liquid chambers, will have no disturbing effect on the course of the hydraulic damping forces. Advantageously, the intermediate space will be vented to the outside, to produce a specific pressure in it.